Can you borrow money in Shmita with a pruzbul ? I understand that prozbul should be written before shmita starts.
You can borrow money in shmitta whether you have a pruzbul or not, it is the lender that will have to forgo the payment of the loan if he does not have a pruzbul. Essentially shmitta annulifies all loans when shmitta finishes, although there are authorities that say that it applies at the beginning of shmitta, and therefore there are some scrupulous people that will also write a pruzbul before the beginning of shmitta, the halacha rmains that it revokes loans at the end.
Rambam Hilchos Shmitta 9, Y:D